A liquid crystal display element included in a liquid crystal display apparatus does not emit light itself. For this reason, the liquid crystal display apparatus includes a planar light source device on a back side of the liquid crystal display element as a light source that illuminates the liquid crystal display element. The liquid crystal display element receives light emitted by a backlight unit, and emits image light. Conventionally, cold cathode fluorescent lamps have been mainly used as light sources of planar light source devices. The cold cathode fluorescent lamp (hereinafter referred to as a CCFL (Cold Cathode Fluorescent)) is a lamp including a glass tube having an inner wall coated with fluorescent substance, and producing white light. However, in recent years, due to drastic improvement in performance of light emitting diodes (hereinafter referred to as LEDs (Light Emitting Diodes)), there is a rapidly growing demand for planar light source devices using LEDs as light sources.
However, light emitted from the CCFL or the LED has poor color purity. Therefore, liquid crystal display apparatuses employing these light sources have a problem that a color-reproduction range is narrow. In this regard, the term “poor color purity” means that light includes a plurality of wavelengths and has low monochromaticity.
Therefore, in recent years, it has been proposed to use a laser with high color purity as a light source of the liquid crystal display apparatus in order to provide the liquid crystal display apparatus having a wide color-reproduction range. Light emitted from the laser has very high monochromaticity. Therefore, a planar light source device using the laser enables providing vivid-color images. In this regard, the term “monochromatic color” means a color having a narrow wavelength width, i.e., a single color with which no other color is mixed. The term “monochromatic light” means single light having a narrow wavelength width.
However, meanwhile, when the laser that emits light having high directivity from a point light source is used as the light source of the planar light source device, it is very difficult to obtain planar light having a spatial light-intensity distribution of high uniformity. The term “point light source” means a light source that radiates light from a single point. Here, the term “single point” means having an area to such an extent that a light source can be treated as a point in an optical calculation without causing any problem in consideration of performance of a product.
A planar light source and a liquid crystal display apparatus described in Patent Document 1 include an optical system including a plurality of optical elements. Light emitted from a laser is shaped by the optical system so that the light has a light intensity distribution in a desired shape. Then, the light emitted from the laser is emitted from the planar light emitting device as planar light having high uniformity.